This invention relates to a bag making and packaging machine for making packages while making bags from an elongated web of a film material and more particularly to such a machine with an improved pressure control for the transverse sealing.
As disclosed in Japanese Patent Publication Tokkai 3-1362, there have been known bag making and packaging machines of the type adapted to pull out an elongated film from a roll, to transport it along a specified path while bending it into a cylindrical form at a downstream position along the path, to seal together its mutually overlapping side edges, to form it into the shape of a bag with the bottom edge transversely sealed between a pair of sealing jaws, to supply articles to be packaged into this bag, to thereafter similarly seal the upper edge transversely and to cut the film to separate the bag, thereby sequentially producing bags with articles sealed therein. With a machine of this type, the transverse sealing of the tubularly formed film is generally effected by means of a pair of sealing jaws disposed opposite to each other across the path of the film and adapted to be brought into contact with the film to thereby heat and seal the tubularly formed film. If the sealing jaws are adapted to move linearly in a reciprocating manner, however, the sealing of the film can be effected only at one point where the jaws come into contact, and the film must be stopped on its path of transportation for a sufficient length of time required for the sealing. Japanese Utility Model Publication Jikko 59-16242 disclosed a system whereby the sealing jaws are each biased by means of a spring in the direction towards the other and are cause to undergo rotary motion in mutually opposite directions including mutually parallel parts such that while the sealing jaws are on these mutually parallel parts of their trajectories, they contact each other against the forces of the springs. Since each jaw moves along a generally D-shaped trajectory, the time of sealing can be made longer while the film continues to move.
Recently, however, use of biodegradable and photodissociable materials is seriously proposed for producing packaging bags for the purpose of protecting the earth's environment. Films of this and other kinds are usually thinner than the film materials which were commonly used in the past. Thus, although prior art films could be sealed at a pressure of several hundred kilograms and it was not necessary to accurately control the sealing pressure, a more precise control is becoming necessary when a film of a more recently developed thinner material is used.
With most of the prior art bag making and packaging machines, however, the sealing pressure was fixed and could not be adjusted according to the kind of film to be used. In the case of a system according to aforementioned Japanese Utility Model Publication Jikko 59-16241, for example, the sealing pressure changes in a fixed manner, being weak during the beginning and final portions of each contacting period of the jaws moving in D-shaped trajectories and stronger in the middle portion. A fine control of the sealing pressure, such as increasing or decreasing it according to the kind of the film or keeping it constant while the jaws are in contact with each other, was beyond its capacity.
Japanese Patent Publication Tokkai 61-190422, on the other hand, disclosed the technology of adjusting the sealing pressure of sealing jaws to a specified target level by controlling a fluid pressure such as air pressure or oil pressure, while Japanese Patent Publication Tokko 8-25542 disclosed a similar technology by controlling the torque of a servo motor. Pressure adjustment by means of a fluid or a servo motor is difficult from the point of view of responsiveness, however, and fine and delicate adjustments and controls are difficult to carry out. The pressure across the sealing surface, furthermore, can be ascertained only by actually measuring it.